Vera was on time. We met by an installation of an enormous Sputnik rocket, the type that had taken Gagarin into space. She was dressed in black and looked very pale, but I was struck by how relaxed and animated she seemed. She kissed me on both cheeks. ‘I congratulate you on your choice of rendezvous,’ she said, with heavy irony.

‘I’m sorry,’ I said, ‘I didn’t remember it being so …’ I gestured at the plastic beer tents, the shashlik vendors, the fairground sideshows, and I fumbled for a word.

‘Yes,’ she said. ‘Poshlyi.’ The word means ‘vulgar’ or ‘common’, but when Vera used it, it expressed a special kind of revulsion, encapsulating a sense of aesthetic and intellectual inauthenticity.

‘How are you feeling?’ I asked.

She shrugged. ‘I tire easily. I am still too weak to fly.’

I suggested we sit down. We walked a few yards to a bench that was sheltered from the drizzle. I watched her check that there was no one in earshot. Above us the rocket stretched up into the thunderous sky.

On the far side of the plaza, a sale of cheap fur coats was taking place in the pavilion that had been built to exhibit the achievements of the Soviet people in the sphere of electricity.

‘Were you followed?’ she asked.

‘Are you serious?’

‘Of course. We are not in London now.’

‘No, I don’t think so.’

‘You said you had questions.’

‘I don’t understand why you left Jack with me. I don’t believe I was your only resource.’

‘You’re right,’ she said. ‘You know the Tyutchev poem?’ She quoted its famous first line: ‘Umom Rossiyu ne ponyat”. It’s the one where he talks about the eternal enigma of Russia: it can’t be comprehended with the mind … it can only be believed. ‘What am I trying to show you has the same quality. You have to experience this truth to believe it.’

I felt an uncanny chill at her words. Tyutchev had been describing a mystery that was ineffably glorious. This, on the other hand, seemed to be shrouded in an obscurity like the fog round a graveyard.

She took a manila envelope from her handbag. ‘I have some things for you.’

Inside was a crumpled mimeograph of an old Soviet research paper, dated 1946, with the text in faded violet ink. Its author was one Yurii Olegovich Malevin.

‘A relative of Sinan’s?’

‘He is Sinan’s father.’ She saw my eyebrows rise at her use of the present tense. ‘He is still alive.’

At the bottom of the envelope I found another piece of paper, soft like old money from repeated foldings. Its age and fragility demanded gentle handling.

It was a photocopy of the identification page from a Kazakh passport. The holder was a Kazakh citizen of Russian origin called Vladimir Efraimovich Trikhonov. He had been born in Baku, Azerbaijan, in 1960. I laid it across my knee.

‘You understand?’ said Vera.

The photograph in the passport had been coarsened by the photocopier that had been used to make it, but it was plain that Trikhonov bore a strong likeness to Jack.

‘Physically, he was Trikhonov,’ she said. ‘In all other ways …’ She paused. ‘He had no recollection of Trikhonov’s identity.’

‘How is that possible?’

‘He underwent … a procedure.’

‘But the language, his mannerisms? The handwriting?’

‘Epiphenomena. By-products of this procedure.’

I told her it was impossible.

She shrugged. ‘You knew him as well as I.’

‘Knew him?’ I said. ‘Knew him?’

‘He is certainly dead by now.’

I don’t recall feeling anything at all. An elderly lady was laying plastic sheets over the racks of cheap Chinese clothes outside the Belorussian Pavilion. My last memories of Jack, sitting up in bed, gripping my arm fiercely and telling me to destroy his journal, seemed more real and more solid than the scene in front of me. I found it impossible to believe Vera, never mind grieve for Jack. ‘How can you be so sure?’ I asked.

‘Nicholas, I am sure,’ she said.

‘I want to be clear about this,’ I told her. ‘You’re saying that Jack was not your brother?’

‘Correct. He was not of my blood.’

Not of my blood. I had a chilling recollection of the cruel needle Bykov had used to sedate him and the drop of blood that had hung from its point.

‘He was this man?’ I held up the photocopy.

‘Yes. Trikhonov was an experimental subject. He volunteered to undergo the Malevin Procedure.’

‘For money?’

‘No. He was a zek. He was serving a life sentence in a penal colony. This was presented to him as an alternative.’

‘So he consented?’

‘This issue of consent is one of many differences I have with Hunter and Sinan. The short answer is yes.’

‘What’s the long answer?’

Vera sighed deeply. ‘Nicholas, suppose I offer you a contract in which you, for a million dollars, agree to sell me your soul? Only superstition would prevent you, correct? You would say, it’s impossible for them to take it, I don’t believe I have a soul, I will take the money. But then you take the money, and I say, “I define the soul as a portion of your limbic system, which I will now remove and you will no longer have your old identity.” Now, you vanish and a totally new person comes into being, with no legal identity of its own, with ill-defined rights, and subject to obligations agreed by someone who no longer exists. Was that contract fair?’

‘Well, I don’t believe such a thing is possible.’

‘That, in a way, is my point. As I understand it, the Native Americans had no concept of the private ownership of land. Result? They lost everything to people who did.’

Vera extended her palm beyond the shelter of the tree to check that the drizzle had stopped. ‘It’s not so mysterious. A plant or a basic mechanical object has a rudimentary consciousness – it responds to external stimuli.’ She passed her hand over some ragged flowers in a tub beside her. ‘These too. And even simple consciousness – grass, a sunflower, a cistern valve – is inscribed with desires. You understand?’

‘A sunflower doesn’t want to turn towards the sun,’ I said. ‘That’s anthropomorphism. That’s what we used to call the pathetic fallacy.’

‘I disagree,’ she said. ‘I think you are simply reluctant to acknowledge the miracle. The miracle is self-consciousness. Recursive consciousness. Consciousness that perceives itself.’

She had lowered her voice. I had to move closer to hear. The aura around her seemed to intensify. I felt as though I was being drawn into her crazy bubble.

‘And where does that come from?’ she asked rhetorically. ‘From language. Logos. Reason – the word – it’s the same thing. Why do you have no memories that precede the acquisition of language? Because before you acquired language, you didn’t exist. There was no you for your experiences to adhere to.’

In the sky to the north-west, the rain clouds had parted. A patch of blue became visible and the sunlight conjured an inappropriate rainbow over the damp pavilions. I had a sudden recollection of the park as it had been: the flowerbeds tended, the exhibits proclaiming the tattered but not yet laughable idea of Soviet superiority.

‘The article I’ve given you was published by Sinan’s father in 1946. It is the theoretical foundation for the procedure which Trikhonov underwent.’

‘Does it work?’

‘Yes, but not exactly as he conceived. Malevin’s ideas were too far ahead of the technological capabilities of his era – like Babbage and Lovelace. But we can now call upon very sophisticated technology for the application of these theories. You know what I mean by a piano roll?’

I told her I did: they’re an antiquated recording technology that captures the melody and dynamics of a particular performance and then allows it to be replayed on a special piano.

‘Conceive, if you can, a piano roll that can listen and respond, both to itself and to the music of an orchestra. It would have the distinctive musical identity of the original pianist, but also the capacity to improvise and embellish. A sophisticated enough version would be indistinguishable from its creator.’